Process of after-tanning with chromium werner type complex



Sept. 3, 1963 J. w. ROBINSON, JR

PROCESS OF AFTER-TANNING WITH CHROMIUM WERNER TYPE COMPLEX Filed March 30, 1956 Pil HIH UHH H l nl l mm mN ww m B 0 R w N H 0 J n ATTORNEY United States Patent 3,102,772 PROCESS OF AFTER-TANNiNG WITH CI-EQMIUM WERNER TYPE COMPLEX JohnW. Robinson, In, Gradyvilie, Pa, assignor to E. I.

du Pont de Neznours and Company, Wilmington, Del.,

a corporation of Delaware Filed Mar. 3%, 1956, Ser. No. 575,006 15 Claims. (El. 894.27)

This invention relates to a process for treating leather to strengthen its defenses against damage by water, perspiration, chemicals and scufling. More particularly the invention is directed to a process of applying to side leather a water-soluble complex compound of the Werner type in which trivalent nuclear chromium atoms are coordimated with carboxylic acido groups having at least 10 carbon atoms. The invention is also directed to iat-liquoring compositions comprising a water-soluble complex compound of the Werner type in which trivalent nuclear chromium atoms are coordinated with carboxylic acido groups having at least 10 carbon atoms.

This application is a continuation-in-part of my copending application Serial No. 520,162, filed July 5, 1955, and now abandoned, which in turn is a continuation-in-part of my parent application Serial No. 351,471, filed April 27, 1 953, and now abandoned.

For the purposes of this invention, the term chrome complex shall mean any water-soluble complex compound of the Werner type in which trivalent nuclear chromium atoms are coordinated with carboxylic acido groups having at least 10 carbon atoms.

In the drawing:

FIGURE 1 is a semi-diagrammatic illustration showing -ly enlarged fibril 1 modified in accordance with a process of the inventionpdifferent portions of the coated fibril 1 shown being cut away.

FIGURE 3 shows in step-wise progression, viewed from left to right, how the two fibrils 1 and 11 of FIGURE 4 are modified by the preferred practice of the invention.

FIGURE 4 is a diagrammatic illustration of the two fibrils 1 and 1 1 in section showing the juncture between them. The small circle A in FIGURE 4 is the basis for the sectional views shown in FIGURE 3.

The inner circle of FIGURE 3 is one illustration of the unique manner in which the chrome complexes 3 and 13 become permanently anchored to the collagen or protein in the leather fibrils 1 and 11. The chromium of the complexes 3 and 13 forms a strong bond with the chrometan or chrome-reactive layers 2 and 12. The organic portions of the complexes 3 and 13 shown as black, rod-like objects in FIGURE 3 are long chain hydrocarbon groups that stick up from the surface of the leather. Much more will be said later about the unique manner in which the chrome complex functions in the present invention.

The mere conversion of raw skin into leather does not generally make it suitable for the various purposes for which leather is used. For some kinds of leather more work is required in the operations following the actual tannage than in the tanning and all preceding operations put together. Each of the innumerable kinds of finished leather require a special series of operations after tanning. One of the most important of these is an operation known as fat-liquoring.

It is upon the eiiiciency of the iat-liquoring and other after-tanning processes that the feel and appearance of the finished leather as well as the strength depends. Too much fat, particularly if it is sulfonated, makes the leather cloth-like, raggy and in some cases greasy or liable to throw ofi the excess in the form of spue as the leather ages. Too little fat-liquor will cause the leather to dry but harsh and to crack when staked or finished in the ordinary way, or at least be too firm even after staking.

In the processing of most leathers, particularly chrometanned leathers, fat-liquoring is absolutely essential. The main purpose of fat-liquoring is to lubricate the small fibers or fibrils l and 11 and so allow them to move over one another freely and easily. This causes the leather to be more flexible. Fat-liquors are also believed to cause a splitting up of the larger fibers into finer ones.

Heretofore, it has not been possible to dry clean fatliquored leathers without a deterioration in general leather properties, such as color, feel, nap characteristics, drape and general overall water resistance.

I have now found that a water-repellent, pliable leather product can be readily obtained which retains its desired leather characteristics even after solvent dry cleaning or mild soap and water washings by using in place of the tat-liquors well known to those skilled in the art a fatliquoring composition containing a chrome complex.

I have further found that a water-repellent, pliable shoe leather product, which is both acid and alkali resistant, can be obtained by applying a chrome complex to sideleather after the leather has been conventionally fat-liquored or concurrently with a conventional fat-liquoring oil, or, less preferably, before a conventional fat-liquor has been applied to the leather.

Leathers treated with fat-liquoring compositions containing a chrome complex but free of the conventional fatliquoring oils retain their desirable characteristics after solvent dry eleanings,'water washings or neutral soap and water washings because of the ability of the complex to react with the free carboxylic acid groups (or amino groups) of the collagen lattice through the coordinate valences of the chrome complex. After further polymerization of the complex-protein reaction product (olation) which takes place on heating or aging of the chrome complex-treated, oil-free leather, this stable chemical combination is no longer afiected by solvent extraction or by emulsifying agents.

The long chain hydrocarbon end of complex 3, by virtue of its hydrophobic properties,'resists the penetration of liquid water 4 into the leather, but allows the passage of 'water vapor. These hydrocarbon ends sticking up from the surface of the leather, as shown in the drawing, also give improved adherence for leather finishes. A more complete disscussion of the merchanisms of the invention will follow.

When conventionally fat-liquored, chrome-tanned side leather is treated in accordance with a process of this invention, the fat-liquor 2b (12b) becomes permanently anchored to the fibrils 1 and ll. The tenacity of this union is remarkable. From a theoretical standpoint, it appears that the Water resistance and other beneficial properties resulting from my novel chrome complex treatment may be due to the long chain hydrocarbon group present in the complex 3 (13), or to improved bonding of the fat-liquor 2b (:lZb) to the leather fibrils '1 [and 11 due to a reaction between the fat-liquor 2b (122;) and the chrome complex 3 (13), or to both.

Not only may there be a reaction between the complex 3 (13) and the collagen or leather protein of the fibrils J1 and 11, but also between the complex 3 (13) and the fat-liquor 2]; (1211). This second reaction may account for the large amount of chrome complex 3 ('13) that may be added to conventionally fat-liquored leathers before the leathers become greasy to the hand.

It is believed that the chrome complex may rearrange in contact with the anionic fat-liquoring oils 2b (12b), sulfated or sulfonated, or even acid dyes, effectively producing a water-resistant, anchored fat-liquoring oil 21; (12b) as well as a dye system. Additionally, chrome complexes 3 and 1-3 of differing carbon contents may have varying degrees of reactivity with anionic fat-liquoring oils 2!) and 12b in the leather. It will be understood, however, that applicant does not limit in any way his invention to this explanation of the mechanism of the invention.

The nature of this invention and more particularly its manner of operation will be more fully discussed following a description of the complexes and other reactants used in the processes of the invention, the leathers which can be treated, and the process conditions which are to be employed.

By the term fat-liquoring oil [I mean to include not only the raw oils, but also the emulsified and/ or sulfated oils used in conventional fat-liquoring of leather. Among the fat-liquoring oils frequently encountered in the production of leather there may be named neats-foot oil, coconut oil, fish oil, sperm oil and castor oil. All of these oils may be compounded with anionic or cationic type emulsifiers. Sulfated forms of such oils can be employed. Other types of oils which fall within may definition of fat-liquoring oils are the non-ionic type such as, for instance, mustard seed oil, teaseed oil, lard oil, corn oil, olive oil, linseed oil, rapeseed oil, soya oil and tallow oil. These non-ionic oils can also be emulsified and/ or sulfated for use in the processing of leather.

The cromium compounds of the Werner type useful for the purposes of my invention are the complex compounds produced by processes in which contact is elfected between carboxylic acids having at least carbon atoms and basic salts of trivalent chromium, the basicity of the chrominum salt being no greater than about 50%. The general methods disclosed in United -States Patents Nos. 2,273,040, 2,356,161 and 2,683,156 are suitable for the prepartion of the complexes useful herein.

Carboxylic acido groups having at least 10 carbon atoms will for convenience of reference hereafter be designated as functional" acido groups. They may be present as simple coordinated groups held by either principal or auxiliary valences or they may be present as bridging groups between two nuclear chrominum atoms.

Particular acido groups may conveniently be designated by adding the suflix -ato to the first part of the name of carboxylic acids corresponding to the acido group. For instance, 'lauric acid gives laurato groups, stearic acid gives stearato groups, abiet-ic acid gives abietato groups, oleic acid gives oleato groups, and napthenic acid gives naphthenato groups.

The functional carboxylic acido groups cordinated with the nuclear chromium atom to make up the principal ingredient of the fat-liquoring compositions of the present invention can be acyclic, carbocyclic, saturated or unsaturated.

' The term acyclic is here used in its ordinary chemical meaning to indicate organic compounds which contain no ring system. For instance, the functional acylic acido groups can be negative groups found in the saturated normal fatty acid having at least 10 carbon atoms. Particularly useful functional groups include capric, undecoic, lauric, tridecoic, myristic, pentadecoic, p'almitic, margaric, stearic, nondecoic, or arachidic acids, or higher acids of this homologous series.

Similarly, the functional acyclic acido groups may be the negative groups of olefinic carboxylic acids having at least 10 carbon atoms. Thus, such acids as undecylenic, myristelenic, palmitolenic and oleic may be used. The functional acido groups may also be derived from carboxylic acids having more than one unsaturated linkage such as linoleic, linolenic, elaeostearic or clupanodonic acids. The functional acido groups may also be derived from carboxylic acids having branched carbon chains in which the total number of carbon atoms in the chain is at least 9.

It is not necessary that the source of the functional acido group be a chemically pure material. In fact, substantial economies may be achieved in many instances by employing naturally occurring mixtures of compounds containing functional acido groups or capable of giving functional acido groups; Functional acido groups may be derived, for instance, from such materials as coconut oil, or hydrogenated coconut oil acids or alcohols, vegetable oils such as cottonseed oil, hydrogenated cottonseed oil, soya bean oil, linseed oil, animal fats and oils, and fish oils.

Various substituted fats and oils may likewise be employed as functional acido groups in preparing the principal constituent of my fat-liquoring compositions, such as, for instance, normal ethanol p-alrnitamide and alphaaminostearic acid. A variety of other sources of acyclic carboxylic acido groups having at least 10* carbon atoms will be readily apparent to those skilled in the art,

By the term carbocyclic is here meant any homocyclic compound of carbon, or in other words, an organic ring compound in which all of the ring atoms are carbon. Typical of the cyclic carboxylic acido groups which can be employed are aryl carboxylic acids having at least 10 carbon atoms such as those having a benzene ring nucleus with carbon chain substitution on the ring, alpha and beta-naphthoic acids, and those having more complicated ring structures such as those derived from phenanthrene. The abietic acid in resin, being methyl-deca-hydroretene carboxylic acid, may be regarded as being of the latter type.

The cyclic groups may be a saturated ring such as occurs in the cyclodecane and its homologues. The ring structure may be aralkyl, containing an aryl group as a substitution in the alkyl group to which the carboxylic group is attached as in the case of naphthyl.

While the functional acido groups which are coordinated with trivalent chromium atoms to give the principal constituent of the fat-liquoring compositions of the invention must contain at least 10 carbon atoms, optimum results are obtained when the number of carbon atoms does not exceed about 25. Groups having more than about 25 carbon atoms [give Werner complex compounds with chromium which are difiicultly water soluble.

The method of making the Werner complexes used in the processes and compositions of this invention, as already indicated, can be generically described a efiecting contact in solution between a carboxylic acido group having at least 10 carbon atoms and basic trivalent chromium salts of monobasic acid, the basicity of the chromium salts being no greater than about 50%. The basic chromium salt is preferably formed in the reaction mixture by reducing a hexavalent chromium compound. Thus, chromyl chloride or chromic oxide can be reduced with an agent such as an alcohol, preferably a secondary alcohol. The alcohol may also function as a solvent for the reaction mixture.

Preferably, the fat-liquoring compositions of the invention contain from about 25 to 30% of the Werner type complex in which a trivalent nuclear chromium atom is coordinated with a carboxylic acid group having at least 10 carbon atoms. The other constituents are lower aliphatic alcohols, ketones, and water.

The Werner complex compounds used in the compositions of my invention are water-soluble. In some instances in order to aid dissolution of the complex compound in water it may be found desinable to dissolve the complex in a non-aqueous solvent such as isopropanol and then form a water solution by dissolving t he non-aqueous solution in water.

The fat-liquoring compositions comprising a complex compound in which trivalent nuclear chromium atoms are coordinated with carboxylic acido groups having at least ten carbon atoms can be applied to any of a variety of leathers. For instance, they may be applied to chrometanned leather, vegetable (extract)-tanned leather, mineral tanned leather, such as aluminum, titanium, Zirconium, iron, etc.; leather tanned with so-called synt-an or sulfonated and sulfated hydrocarbons and leather tanned with copolymers of styrene and maleic anhydride, and combinations of the above.

It will naturally be necessary to adapt the fat-liquoring process to the type of leather to be treated. For instance, the period of drumming sheepskin suede leather with the fat-liquor compositions of the invention will be substantially less than that required for drumming side leather. Such adaptations as this can be readily made by those skilled in the art in order that the compositions of this invention meet the specific needs of specialized problems.

Leather to be fat-liquored according to the processes of this invention may be prepared in accordance with any of the conventional tannery practices. P or instance, raw sheepskin may be put thru the conventional steps of degreasing, chrome tanning, fleshing, wet wheeling, mordanting (with extract) and drying preparatory to being dyed and fat-liquored. Raw hide such as cowhide can be put 'thru the customary processing steps of soaking, liming,

unhairing, hating, piclcling \ohrome and/:or vegetable tanning, sorting, splitting to weight and shaving to even. The side leather is then ready to be fat-liquored and colored if necessary.

it is also possible to add after the mordanting step a the intermediate drying step preparatory to being dyed and fat-liquored with a complex chromium compound.

It is also possible to add after the mordanting step a synthetic resin such as styrene-maleic anhydride tanning agent as a filler and also eliminate the conventional timeconsuming drying step, going directly to the fat-liquoring processes of this invention.

In the processing of side leather a retannage involving a small amount of vegetable extract 2b (1%) or a resin 2b (12b) after the chrome tanning 2a (12a) step is preferred. This assures better penetration of the chorme complex 3 (13) and exhaustion of it from the fat-liquoring composition. Most fat-liquors except possibly those of the alkaline types can be employed without dificulty. However, it will be understood that wetting agents should not be used.

While I have described sheepskin and side leather, it will be readily recognized that the processes of this invention can be applied to other types of skins being processed into finished leather such as calfskin, kidskin, horse, pigskin, deerskin, kangaroo, Chamois, kip and the like.

While leather prepared in any manner may be treated according to the processes of this invention, the pH of the leather is important. It will generally be found desirable to have the leather at a pH of from about 4 to 5 although leathers having pH as low as 2.5 or lower can be satisfactorily fat-liquored in accordance with my invention.

It will be understood that the leather may be fatliquored with the chorme compositions prior to, or subsequent to dyeing, or partially at each of these times.

The considerations as to the type of apparatus to use, the time to be allowed for fat-liquoring, the temperature of fat-liquoring, and the amounts of fat-liquoring composition are substantially those known to the art in connection with prior art fat-liquoring processes.

The time allowed for fat-liquoring with a complex chromium compound should be sufiicient to permit substantial exhaustion of the fat-liquoring composition. With sheepskin suede, for example, a period of at least 30 minutes is recommended for practical usage. Generally the period for fat-liquoring sheepskin suede will not ex ceed 1 /4 hours. The preferred time for fat-liquoring side leather with a carboxylate chromic chloride is from about /2 hour to 2 /2 hours.

The fat-liquoring can best be effected at temperatures of from about 70 to about 130 F. but temperatures outside this preferred range can successfully be employed if desired. In the case of suede leathers, the leather follOWing dyeing is preferably washed at -130 F. prior to treatment in accordance with the present invention in order to eliminate foam, to improve dye levelness by removing unreacted dye, and to adjust the leather to the proper temperature.

The leather is floated in water according: to conventional practice following washing and drainage. The exact amount of water to use can best be determined by a few simple tests under the specific conditions of the process selected and with the specific leather to be treated. High floats such as 8 parts of water per 1 part of leather (over gal. percent) may be used. Low floats, say 4 parts of water to 1 part of leather, are also satisfactory.

The exact amount of the fat-liquoring composition to use is readily determined by a few simple experiments under the precise conditions selected and with the specific leather to be treated. For fat-liquoring sheepskin suede the preferred amount of fat-liquoring composition containing about 30 percent of the Werner-type chromium complex to be used ranges front about 10 to about 25 percent by weight based on dry leather. On a basis of wet weight of the leather the chromium complex is applied in concentration of from about 5 to 15 percent. For side leather, 10 to 40 percent by weight of the fat-liquoring composition is preferably employed. In general, enough of the fat-liquoring composition must be used to effect the fat-liquoring desired but unduly large amounts should not be usd as they will not be taken up by the leather in a reasonable period.

In order to avoid local action and waste, the fat-liquor ing compositions are generally diluted with water before they are added to the leather.

It will be understood that fat-liquoring compositions containing a chromium compound of the Werner-type may be used together with raw oils such as, for instance, mineral oil and neats foot oil to enhance color value, or in the case of side leather to supplement the fat-liquoring effect of the Werner type chrome complex. The Werner type chrome complexes in my fat-liquoring compositions serve as cationic emulsifying agents for the raw oil. The raw oil is added to the chrome complex and the resulting mixture then added to the water system.

As already indicated, acid and alkali resistant, Water repellent leather can be produced by first treating the tanned skins with conventional fat-liquors and then applying a chrome complex of the type described above. In this fat-liquoring operation the range of concentrations of the fat-liquoring oils is from about /2 to about 6 percent. However, in some instance the total concentration of fat-liquors may be as high as 20 percent based on the wet weight of the leather. The limiting; factors on oil concentration is maintenance of water resistance and softness of the leather. An excessive amount of oil causes the leather to be too soft.

A typical operating procedure for applying chrome complex to a conventionally fat-liquored side leather consists of the following three steps:

(1) After the last wet operation (dyeing or fat-liquoring) the drum is drained and a new float is introduced at about 100 F. and adjusted to a pH of from 3 to 3.5 with a monobasic acid such as formic acid. These conditions are necessary to limit the reaction rather than to allow the proper penetration of the complex throughout the hides.

(2) The chrome complex is then added in an amount equal to 6 to 10% of the weight of the skins after splitting and shaving.

(3) The skins are drummed for from 30 minutes to 1 hour. The time actually required will be dependent upon the type of drainage employed.

Alternatively, the chrome complex can be: applied to the tanned leather prior to, or concurrently with, conventional fat-liquors. Such fat-liquors may be of the cationic, anionic or nonionic type. The resulting leather is water-repellent, alkali and acid resistant.

' water.

Upon exhaustion of the chrome complex composition, it is preferred to wash the leather with room temperature The purpose of this washing is to remove unreacted chrome complex compound, dye and any possible side reaction product between dyestulf and chrome complex. If foam is present, it is readily removed by such washing.

As indicated above, the leather to be iat-liquored with a chrome complex may be dyed with any of a wide variety of dyestuffs customarily used in the art and treated with conventional finishing compositions to obtain commercially acceptable leathers.

Leather treated in accordnace with the processes of my invention finds wide usage in leather garments, shoes, gloves, gaskets, belting, luggage and the like.

The leather obtained according to the present invention has a satisfactory handle or feel comparable to leather produced solely with conventional fat-liquors. The leather is not greasy. Further, the leather is water resistant but still permeable to moisture vapor.

Leather obtained using a Werner type chromium compound of at least 10 carbon atoms as the sole fat-liquoring agent is also resistant to dye bleeding both in Water and solvents, the former being of importance in the normal wear of the garment; while the latter is of importance in preventing dye. fading or washout when the garments, particularly those of suede, are dry-cleaned. Thus, leather fat-liquored without use of conventional f atliquoring oils retains its good appearance and feel after solvent dry cleanings.

The water resistant properties of the leather produced by the process of the present invention were measured by a dynamic absorption test involving a 20-minute immersion in water at 80 F. conventionally fat-liquored leather absorbs approximately 150-200 percent water in this test, but leather fat-liquored with the compositions of this invention absorb only 20-50 percent water. The water absorbtive capacity of leather fat-liquored with chrome complexes alone remains substantially unchanged after 3 cleaning cycles with dry cleaning solvent or neutral soap and water at 120 F.

Side leather produced by a process comprising (1) chrome tanning hides of steer, cow, or kip, (2) re-tanning with from 3 to 50 percent of quebracho crystals or extract (or wattle, chestnut or combination of syntans such as styrene-maleic anhydride, and wood extracts), (3) fatliquoring with conventional fat-liquors, (4) dyeing. and (5) finally applying a chrome complex of at least carbons, is outstanding in its resistance to chemicals. For example, such leather is resistant to 98 percent sulfuric acid, 70 percent nitric-acid, 85 percent lactic acid, 36 percent hydrochloric acid, 25 percent caustic, concentrated ammonia, nitrobenzene and the like. The resistance of such leather to lactic acid, which is present in perspiration, makes the leather of particular 'value in the inner sole field and in the manufacture of white shoes such as those worn by nurses. Such side leather is also useful for safety shoes and for farmer shoes and boots in View of their repeated exposure to manure and urine.

Actual wearatests of matched pairs of shoes-one made of leather treated with a chrome complex in accordance with the invention and the other of untreated leatherclearly shows that a chrome complex having at least 10 carbon atoms imparts properties to side leather which are more important than 'water resistance alone.

Side leather treated with a chrome complex in accordance with the invention gives consistently a tighter grain structure. This factor of tighter grain structure promises to enable the tanner to produce a higher percentage of high-quality and shoes made of this leather keep their good appearance longer.

Shape retention or dimensional stability is another characteristic common to side leather treated in accordance with this invention. A chrome complex treated shoe keeps its shape and fit, while the untreated shoe stretches, tears out stitches, and loses its fit, comfort and appear- 8. ance. In the shoe factory dimensional stability promises to reduce rejections and to increase the efiiciency of workmen.

Still another characteristic common to side leather treated with chrome complex according to the invention is better finish. In wear-tests, this shows up as less tendency to scuff. Polishing tends to give the leather a more pleasing appearance, even after severe wear. In the tannery, finish adheres better to leather treated with chrome complex, and the leather appears to take less finish to give desired coverage. In [manufacturing shoes, improved adhesion of the finish promises fewer rejections and better efliciency.

As has already been indicated, resistance to chemicals such as strong acids and bases is particularly conspicuous in leather treated with a chrome complex according to the present invention.

Resistance to perspiration is another feature of such leather. When swatches of chrome-tanned, vegetableretanned leather were subjected to 9 cycles of synthetic perspiration by a procedure recommended by the Thin ners Council Research Laboratory, the swatch without chrome complex treatment broke when flexed the first time, while the treated one remained pliable and strong even after 8,000,000 flexes. Likewise, in the Gustafson perspiration test procedure, the leather which was processed with a chrome complex in accordance with the process of my invention maintained its original properties, while the untreated material was destroyed when subjected to one cycle of the aforementioned test PTO-1 cedure.

As already indicated, Water resistance is an important characteristic of the side leather which has: been treated with a chrome complex. Shoes made from leather treated with a chrome complex absorbed only 14 to 18% of their dry weight. In contrast, shoes made of comparable leather without the complex absorbed 80 to 100%. In manufacturing shoes, the factor of water resistance carries with it the promise of greater stability as to moisture content, fewer rejections and higher efficiency.

The processes of the invention can be more fully understood by further reference to the drawing. There is shown in FIGURE 1 a cross section of a swatch of leather which has been subjected to one of the processes of the invention. The wavy lines represent fibrils or small leather fibers. It will be noted that there are many more fibrils near the surface or top of the leather. But regardless of their particular position in the swatch, the individual fibrils are substantially identical.

As has already been indicated, FIGURE 2 is an enlarged view of a typical fibril of FIGURE 1. It illustrates a modified fibril in which the collagen (leather protein) of the fibril 1 has been chrome-tanned, optionally retanned, fat-liquored with a conventional oil, and then with a chrome complex 3 according to the invention. The collagen core 1 is surrounded with a chrome-reactive layer 2, which in turn may be composed of several distinct sublayers or envelopeschrome tan layer 2:; and layer 2b resulting from a vegetable extract retannage or from fat-liquoring with an anionic agent. Finally, an outer coating of chrome complex 3 surrounds intermediate shell 2 which in turn envelops the fibril 1.

The circles in FIGURE 3 give a diagrammatical comparison of fibrils 1 and 11 before and after treatment according to processes of the invention.

The circle at the extreme left of FIGURE 3 is an enlarged view of the inner circle A of FIGURE 4 and shows the two individual fibrils 1 and 11 in section near the juncture of the two. The fibrils in this circle have not been tanned or treated in accordance with the invention. The small space 5 between the fibrils 1 and 11 is a void into which only a very limited amount of air or water vapor can penetrate. Hides composed of bundles of such fibrils are unworkable.

The second circle of FIGURE 3 shows two fibrils 1 and 111 of A of FIGURE 4 in a similar position but this time the skin substance has been tanned with chrome and the fibrils 1 and 11 are coated with chrome layers 2 and 12. Water 4 is shown to have penetrated into the void between the two fibrils l and 11. Accordingly, this circle illustrates the prior art.

The center or middle circle of FIGURE 3 is a View of two fibrils 1 and 11 which have been tanned and the chrome-tanned layers 2 and 12 coated with chrome complexes 3 and 13 according to the invention. No aqueous layer is present between fibrils 1 and 11 but there is still sufficient space between fibrils 1 and 11 for water vapor to pass thru. In other words, the leather containing such fibrils is water-repellent but it can breathe.

The chromium in the chrome complexes 3 and 13 is shown as a circle at the end of the black bar, the solidinked bar representing the organic tail or hydrocarbon end of the complex. The chromium is chemically bound to the collagen of the fibrils 1 and 11 thru the chrome or chrome-reactive layer 2. The bond is so firm that the complex 3 stays anchored to layer 2 which in turn permanently envelopes the fibril core 1. This chemical union of chromium to the chrome-reactive layer 2 (shown in the fourth circle of FIGURE 3 as chrome-tan layer 2a and anionic modifier layer 2b) aids in the permanent lubrication of the leather fibrils. This means the fibrils move smoothly when the leather is flexed and hence cnacking is reduced. The organic portions of the chrome complex 3 or 13 are long chain hydrocarbon groups that stick out from the surfaces of fibrils 1 and 11, giving them water resistance and better adherence for leather finishes. By virtue of their hydrophobic properties these hydrocarbon ends resist the penetration of liquid water into the void between fibrils 1 and 11 but allow for the passage of water vapor therebetween.

In the fourth circle of FIGURE 3, viewed from left to right, there is shown in cross section fibrils 1 and 11 which have been treated in accordance with a preferred process of the invention. The fibrils have been tanned with chrome 2a and 12a and then subjected to a treatment with an anionic fat-liquor 2b and 12b preferably after retannage with a vegetable extract.

The remaining circle of FIGURE 3 illustrates the non water repellency of the two fibrils 1 and 11 which have been tanned 2a and 12a, retanned and fat-liquored with conventional oils 2b and 12b but not treated according to my invention. Instead of the fibnils 1 and 11 being enclosed in an outer shell of a chrome complex, they are merely covered with chrome tan layers 2a and 12a and chrome-reactive (anionic modifying) layers 2b and 12b. These fibrils possess none of the beneficial properties of the fibrils of circles three and four which are enclosed in a unique chrome complex layer such as 3 or 13.

It will be understood that the above explanation of the mechanism of the preferred processes of the invention is based on the best data available to the applicant. The results of the invention are, however, independent of such explanation.

Reference should now be had to the following illustrative examples:

Example 1 Chrome tanned sheepskin suede leather in a crusted condition without fat-liquor is wet back with water and in some cases wetting agent and dyed according to standard leather practices. The final pH of the leather is about 4.0.

After the washing operation is completed following dyeing, the leather is allowed to drain completely. The temperature of the wet leather is about 120 F.

The wet but drained colored sheepskin leather is floated in water using four gallons of water per /2 dozen skins. The water used is at room temperature. The V2 dozen skins weigh about 6 pounds dry. One and one-half 10 pounds of fat-liquoring composition containing 30% by weight stearato chromic chloride is diluted with 1 gallon of room temperature water and added to the floated leather in a drum or paddale wheel.

The leather is drummed in the stearato chromic chloride solution for a period of about 30 minutes. Optionally, it can be run until maximum exhaustion takes place.

After exhaustion, the leather is drained, washed at room temperature, drained again, set out and dried in the conventional manner. Following drying, the leather is finished in a conventional fashion to give dry-cleanable, water-resistant, pliable leather product.

Example 2 Six parts by dry weight of chrome tanned side leather following splitting and shaving is treated with quebracho extract in water according to standard leather practice. The leather is allowed to drain. The drained extracttreated side leather, adjusted to pH 2.5 with hydrochloric acid, is floated in water.

About 2 parts by weight of fat-liquoring composition containing about 30% stearato chromic chloride and 6% raw neats-foot oil are diluted with 4 parts of water and added to the floated leather. The leather is drummed in the stearato chromic chloride solution for about 2 hours. After the solution is exhausted, the leather is drained, set, dried and finished in a conventional manner. The resulting leather is water-resistant.

Example 3 Sheepskin suede leather is fat-liquored in a manner identical with that described in Example 1, except that a fat-liquoring composition containing palmitato chromic chloride is employed instead of stearato chromic chloride. The resulting leather is dry-cleanable and has bleed resistance in water and solvent.

Example 4 Fat-liquoning of sheepskin suede leather is effected in a manner similar to that described in Example 1 using oleato chromic chloride. The resulting leather is waterrepellent, pliable and mellow.

Example 5 Ten parts by weight of conventional army retan leather Fat-liquoring of sheepskin suede leather is effected in a manner similar to that described in Example 1 using abietato chromic chloride. The resulting leather is very water resistant and pliable. Similar results are obtained with fat-liquoring compositions containing individually or jointly such Werner type complexes as for instance caprato chromic chloride, laurato chromic chloride and a complex prepared by reacting basic chromic chloride with a mixture of saturated fatty acids having 20 or more carbon atoms.

Example 7 Cowhide is chrome tanned by drumming the hide with 7 percent basic chrome sulfate containing 22.5 percent Cr O for a period of four hours. Sodium bicarbonate (1 /2 percent) is added to the hide to fix the chrome in the hide. The hide is then drummed for one hour to obtain penetration of the sodium bicarbonate. The hide is drained, washed and pulled out of the drum. The

leather'is split to the desired thickness. wet back.

Twelve percent of quebracho extract based on the split shaved weight of the skins is added. The resulting mixture is drummed for a period of one hour. Ten percent based on split shaved weight of a composition consisting essentially of sulfated neats-foot and sulfated cod oil is added as a fat-liquor. rFat-Iiquoring requires about one hour. One percent egg yolk is added, and the mixture run 20 minutes. After drainage the leather is dyed, the dye being added in amount of 2 percent based on split shaved weight. The leather is then run and set with formic acid. It is drained and rinsed to adjust the temperature to 100 -F. An isopropanol solution of stearato chromic chloride having a water content of from '3 to 6 percent by weight of the solution is added in an amount based on split shaved weight of about percent. The leather-chrome complex solution is drummed for one hour. The leather is removed and found to be waterresistant, acid-resistant and alkali-resistant.

The skins are Example 8 In a manner substantially identical with that described in Example 7, cowhide is chrome tanned with 8 percent Tanolin R, retanned with 12 percent quebracho extract, fat-liquored with a composition containing 10 percent by split shaved weight of sulfated neats-foot combined with sulfated fish oil and 1 percent egg yolk. The fatliquored leather was dyed and finally treated with stearato chromic chloride in aqueous isopropanol. Based on the split shaved weight of the leather, the amount of chrome complex commodity (isopropanol solution of stearato chromic chloride containing 6 percent chromium) applied to the leather was about 10 percent. The resulting leather is well suited for shoe uppers.

Example 9 Using a tanning process related to that described in Example 7, steer hide is tanned with 6 percent Tanolin R, retanned with a mixture consisting of 7 percent quebracho and 7 percent wattle, dyed, fat-liquored with a composition consisting of. 2 percent cationic sperm oil, 4 percent sulfated fish-oil, and 2 percent emulsified fish oil. To this fat-liquored leather, 7 percent Quilon chrome complex is added to render the leather waterresistant, acidand alkali-resistant.

I claim: 7 e

1. In an after tanning process for treating leather the step which comprises lubricating the leather by applying thereto a composition containing as an essential ingredient a Werner complex compound in which a trivalent nuclear chromium atom is coordinated with a carboxy-lic acid group having at least 10 carbon atoms at a temperature and for a time sufficient to eifect lubricating of said leather.

2. In an after-tamiing process for treating leather, the step which comprises applying to the leather a fat-liquoring composition containing as an essential active fatliquoring ingredient a Werner complex compound in which a trivalent nuclear chromium atom is coordinated with a carboxylic acido group having from 10 to about 25 carbon atoms, at a temperature and for a time sufficient to effect fat-liq'uoring of said leather.

3. The method of fat-liquoring leather which comprises applying to already tanned leather a fat-liquoring composition compnising up to based on the wetweight of the leather of a Werner complex compound in which a trivalent nuclear chromium atom is coordinated with a carboxylic acido group having from 10 to about carbon atoms, at a temperature from about 70 to 130 F. for about one-half to two and one-half hours.

4. In an after-tanning process for treating leather, the step. which comprises applying to the previously tanned leather a fat-liquoring composition comprising a fatliquoring oil in an amount up to about 20% based on the wet weight; of the leather and, in an amount up to 12 about 40% based on the wet Weight of the leather, a Werner complex compound in which a trivalent nuclear chromium atom is coordinated with a carboxylic acido group having from 10 to about 25 carbon atoms, at a temperature from about 70 to F. for a period of one-half to two and one-half hours.

5. In an after-tanning two-step process for fat-liquoring leather, the steps which comprise as a first step applying to the tanned leather a Werner complex compound in which a trivalent nuclear chromium atom is coordinated with a carboxylic acido group having from 10 to about 25 carbon atoms and thereafter as a second step applying to the treated leather a fat-liquoring oil, the twostep treatment being carried out at a temperature and for a total time sufiicient to eifect fat-liquoring of said leather.

'6. in an after-tanning two-step process for treating leather, the steps which comprise as a first-step applying to the leather a fat-liquoring oil in an amount up to about 20% based on the wet weight of the leather, and thereafter as a second step applying to the oil-tneated leather, in an amount up to about 40% based on the wet weight of the leather, a Werner complex compound in which the trivalent nuclear chromium atom is coordinated with a carboxylic acido group having from 1 0 to about 25 carbon atoms, the two-step treatment being carried out at a temperature and for a total time sufiicient to efiect fat-liquoring of said leather.

7. The method for effecting the fat-liquoring of already tanned leather whichv comprises applying to the leather a fat-liquoring composition containing as an essential active fat-liquoring ingredient a Werner complex compound in which a trivalent nuclear chromium atom is coordinated with a carboxylic acido group having from 10 to about 25 carbon atoms, the concentration of the Werner complex compound and the duration and temperature of the treatment being suflicient to impart fatiliquoring properties to said leather.

8. In an after-tanning process for treating leather, the step which comprises applying to the leather, while the leather is at a pH of from about 2.5 to 5, a fat-liquoring composition containing as an essential fat-liquoring ingredient at Werner complex compound in which a trivalent nuclear chromium. atom is coordinated with a carboxylic acido group having from 10 to about 25 carbon atoms, at a temperature and for a time suiflcient to effect fat-liquoring of said leather.

9. In an after-tanning process for treating leather, the step which comprises applying to the already tanned leather a fat-liquoring composition containing as an essential' fat-liquoring ingredient a Werner complex compoundin which a trivalent nuclear chromium atom is coordinated with an acyclic carboxylic acido group having from 10 to about 25 atoms, at a temperature and for a time sufiicient to effect fat-liquoring of said leather.

,10. Inan after-tanning process for treating leather, the step which comprises applying to the already tanned leather a fat-liquoring composition containing stearato chromic chloride, at a temperature and for a time sulficient to effect fat-liquoring of said leather.

11. In an after-tanning process for treating leather, the step which comprises applying to the already tanned leather a fat-liquoring composition containing myristato chromic chloride, at a temperature and for a time sufiicient to effect fat-liquoring of said leather.

12. In an after-tanning process for treating leather, the step which comprises applying to the already tanned leather 2. fat-liquoring composition containing oleato chromic chloride, at a temperature and for a time suflicient to effect fat-liquoring of said leather.

13. An after-tanning process for treating leather, the step which comprises applying to the already tanned leather a fat-liquoring composition containing as an essential fat-liquoring ingredient a Werner complex compound in which a trivalent nuclear chromium atom is coordinated with a carbocyclic carboxylic acido group hav- 13 ing from 10 to about 25 carbon atoms, at a temperature and for a time suflicient to effect fat-liquoring of said leather.

14. In an after-tanning process for treating leather, the step Which comprises applying to the already tanned leather a fat-liquoring composition containing abietato chromic chloride, at a temperature and for a time sutficient to effect fat-liquoring of said leather.

15. A composition of matter comprising a fat-liquoring oil and as an essential fat-liquoring ingredient a Werner complex compound in which trivalent nuclear chromium atoms are coordinated with earboxylic acido groups having from 10 to about 25 carbon atoms, said fat-liquoring oil and said Werner complex compound to- References Cited in the file of this patent UNITED STATES PATENTS 2,071,567 Pansel Feb. 23, 1937 2,136,433 Gasnier Nov. 15, 1938 2,273,040 Iler Feb. 17, 1942 2,381,752 Iler Aug. 7, 1945 2,437,044 Robinson et a1 Mar. 2, 1948 

1. IN AN AFTER TANNING PROCESS FOR TREATING LEATHER THE STEP WHICH COMPRISES LUBRICATING THE LEATHER BY APPLYING THERETO A COMPOSITION CONTAINING AS AN ESSENTIAL INGREDIENT A WERNER COMPLEX COMPOUND IN WHICH A TRIVALENT NUCLEAR CHROMIUM ATOM IS COORDINATED WITH A CARBOXYLIC ACID GROUP HAVING AT LEAST 10 CARBON ATOMS AT A TEMPERATURE AND FOR A TIME SUFFICIENT TO EFFECT LUBRICATING OF SAID LEATHER. 